Table 4 Total Influenza positive Influenza negative Vaccinated 32 368 400 Not vaccinated 90 510 600 Total 122 878 1000 23. Following from question 21, we are conducting a six-month long observational prospective cohort study, and obtain the data shown in Table 4. Calculate and interpret a risk difference comparing the risk in the whole population as observed, and a counterfactual situation in which everyone in the population obtained the vaccine. For the purposes of this calculation only, you may assume that the 2x2 table is unbiased (including: assume there is no confounding) and therefore that the observed risk in the vaccinated can stand in for the risk in the whole population if everyone were vaccinated; and that the risk in the unvaccinated can stand in for the risk in the whole population if everyone were unvaccinated